﻿using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Reflection;

namespace Paas.Pioneer.Domain.Shared.Helpers
{
	/// <summary>
	/// 枚举扩展
	/// </summary>
	public static class EnumUtil
	{
		// 枚举显示字典缓存
		private static  ConcurrentDictionary<Type, Dictionary<int, string>> EnumDisplayValueDict = new ConcurrentDictionary<Type, Dictionary<int, string>>();

		// 枚举值字典缓存
		private static  ConcurrentDictionary<Type, Dictionary<int, string>> EnumNameValueDict = new ConcurrentDictionary<Type, Dictionary<int, string>>();

		// 枚举类型缓存
		private static ConcurrentDictionary<string, Type> _enumTypeDict = null;

		/// <summary>
		/// 获取枚举对象Key与名称的字典（缓存）
		/// </summary>
		/// <param name="enumType"></param>
		/// <returns></returns>
		public static Dictionary<int, string> GetEnumDictionary(Type enumType)
		{
			if (!enumType.IsEnum)
				throw new Exception("请选择正确枚举类型");

			// 查询缓存
			Dictionary<int, string> enumDic = EnumNameValueDict.ContainsKey(enumType) ? EnumNameValueDict[enumType] : new Dictionary<int, string>();
			if (enumDic.Count == 0)
			{
				// 取枚举类型的Key/Value字典集合
				enumDic = GetEnumDictionaryItems(enumType);

				// 缓存
				EnumNameValueDict[enumType] = enumDic;
			}
			return enumDic;
		}

		/// <summary>
		/// 获取枚举对象Key与名称的字典
		/// </summary>
		/// <param name="enumType"></param>
		/// <returns></returns>
		private static Dictionary<int, string> GetEnumDictionaryItems(Type enumType)
		{
			// 获取类型的字段，初始化一个有限长度的字典
			FieldInfo[] enumFields = enumType.GetFields(BindingFlags.Public | BindingFlags.Static);
			Dictionary<int, string> enumDic = new Dictionary<int, string>(enumFields.Length);

			// 遍历字段数组获取key和name
			foreach (FieldInfo enumField in enumFields)
			{
				int intValue = (int)enumField.GetValue(enumType);
				enumDic[intValue] = enumField.Name;
			}
			return enumDic;
		}

		/// <summary>
		/// 获取枚举类型key与描述的字典（缓存）
		/// </summary>
		/// <param name="enumType"></param>
		/// <returns></returns>
		/// <exception cref="Exception"></exception>
		public static Dictionary<int, string> GetEnumDescDictionary(Type enumType)
		{
			if (!enumType.IsEnum)
				throw new Exception("请选择正确枚举类型");

			// 查询缓存
			Dictionary<int, string> enumDic = EnumDisplayValueDict.ContainsKey(enumType) ? EnumDisplayValueDict[enumType] : new Dictionary<int, string>();
			if (enumDic.Count == 0)
			{
				// 取枚举类型的Key/Value字典集合
				enumDic = GetEnumDescDictionaryItems(enumType);

				// 缓存
				EnumDisplayValueDict[enumType] = enumDic;
			}
			return enumDic;
		}

		/// <summary>
		/// 获取枚举类型key与描述的字典（没有描述则获取name）
		/// </summary>
		/// <param name="enumType"></param>
		/// <returns></returns>
		/// <exception cref="Exception"></exception>
		private static Dictionary<int, string> GetEnumDescDictionaryItems(Type enumType)
		{
			// 获取类型的字段，初始化一个有限长度的字典
			FieldInfo[] enumFields = enumType.GetFields(BindingFlags.Public | BindingFlags.Static);
			Dictionary<int, string> enumDic = new Dictionary<int, string>(enumFields.Length);

			// 遍历字段数组获取key和name
			foreach (FieldInfo enumField in enumFields)
			{
				int intValue = (int)enumField.GetValue(enumType);
				var desc = enumField.GetDescriptionValue<DescriptionAttribute>();
				enumDic[intValue] = desc != null && !string.IsNullOrEmpty(desc.Description) ? desc.Description : enumField.Name;
			}
			return enumDic;
		}

		/// <summary>
		/// 从程序集中查找指定枚举类型
		/// </summary>
		/// <param name="assembly"></param>
		/// <param name="typeName"></param>
		/// <returns></returns>
		public static Type TryToGetEnumType(Assembly assembly, string typeName)
		{
			// 枚举缓存为空则重新加载枚举类型字典
			_enumTypeDict ??= LoadEnumTypeDict(assembly);

			// 按名称查找
			if (_enumTypeDict.ContainsKey(typeName))
			{
				return _enumTypeDict[typeName];
			}
			return null;
		}

		/// <summary>
		/// 从程序集中加载所有枚举类型
		/// </summary>
		/// <param name="assembly"></param>
		/// <returns></returns>
		private static ConcurrentDictionary<string, Type> LoadEnumTypeDict(Assembly assembly)
		{
			// 取程序集中所有类型
			Type[] typeArray = assembly.GetTypes();

			// 过滤非枚举类型，转成字典格式并返回
			Dictionary<string, Type> dict = typeArray.Where(o => o.IsEnum).ToDictionary(o => o.Name, o => o);
			ConcurrentDictionary<string, Type> enumTypeDict = new ConcurrentDictionary<string, Type>(dict);
			return enumTypeDict;
		}
	}
}